Several cover crops (CCs) exert allelopathic effects that suppress weed growth. The aim of the present study was to evaluate the effects of aqueous extracts containing different concentrations 0, 0.5, 1, 2.5, 5, 7.5 and 10% ( / ) of Brassicaceae CCs ( and of the CCs and on germination and early growth of L. The allelopathic effects were species and concentration-dependent. , for example, caused the greatest potential to inhibit germination, shoot, radicle length and fresh seedling weight, whereas and inhibited germination and early growth of only at concentrations ≥7.5%. In contrast, no inhibition was observed when aqueous extracts of and were added at any of tested concentration. Liquid chromatography-tandem mass spectrometry detected 15 phenolic compounds in Brassicaceae CCs with the highest content (µg/g) of vanillin (48.8), chlorogenic acid (1057), vanilic acid (79), caffeic acid (102.5) and syringic acid (27.3) in . Our results suggest that is the most allelopathic CCs and that the fruits of are the plant organs richest in allelochemicals.